The present invention is directed to a connector assembly for connecting optical fibers for use in optical communication systems, and particularly to a flexible ferrule device for connecting optical fibers for such use. The present invention further relates to a method of connecting optical fibers using such a device and to a tool for use thereof.
The invention relates to an optical fiber connection device that allows for the end-to-end alignment of two optical fibers in a way such as to permit a light signal to pass from one fiber to the other fiber with minimal attenuation and reflection losses. This device also makes it possible to reduce any air layer between the ends of the two fibers in contact by maintaining pressure on their ends.
Ferrules and related technology are known in fiber optic connection. The art is replete with examples, including U.S. Pat. Nos. 6,579,015; 6,533,469; 6,416,236; 6,357,933 and U.S. Patent Application Publication No. 2002/0037140 entitled “Composite Ferrule of Connector for Optical Fibers and Methods of Manufacturing same”. A ferrule for use as a connector in an assembly with optical fibers requires high dimensional accuracy and precision, yet in an extremely small-diameter conduit for positioning and holding optical fiber. Present or proposed ferrule connectors for optical fibers, such as U.S. Pat. No. 6,357,933 to Lucent Technologies Inc. may not be amenable to ease of manufacture or assembly with optical fiber by the technical personnel carrying out the operation. Thus, in spite of the known application of ferrules in optical fiber connection, there is a continuing need for improvement in the technology of the design and use of ferrules for this purpose. For example, relating to aspects of attenuation and return loss, the establishing of as perfect as possible fiber-to-fiber contact between end portion of optional fibers and the prevention of face dust accumulation between the fiber faces. There is also a need to improve the ease of use of ferrules in an assembly for connection of optical fibers in an optical communication system, by the person carrying out the operation.
Optical fibers are generally made of glass or polymers and are made of successive and concentric layers. At the inner centre of the fiber, one can find the core of the fiber. The core is surrounded by the cladding. Both constitute the wave-guide that will conduct light. They are made of glass for better performance, and thus they are fragile.
The cladding is generally coated with a polymer layer that protects the glass from scratches and allows the optical fiber to bend, or to exert tensile strength on it. The last layer of protection is called the buffer.
For example, the diameter of the core can be between 6 to 60 μm and the diameter of the cladding is generally 125 μm, but can be 50 μm to 200 μm. The buffer diameter is generally 250 μm for fibers to be assembled in a cable with other optical fibers. If used alone, a fiber will receive a 900 μm buffer made of different layers to protect glass and polymers from water and sunlight.
In the field of photonics, optical fibers are used for the transmission of optical signals as well as for the linking of optical switches, waveguide grating devices, optical amplifiers, modules and the like. Optical transmission systems relying on photonics have been taking on greater importance, as optical signals are capable of carrying a far larger quantity of information as compared to typical copper wire communication systems. For example, with the technology of Dense Wavelength Division Multiplexing (DWDM) and Demultiplexing it is possible to transmit multiple wavelengths in a single fiber, providing data capacities of 40 Gigabits per second and greater.
Optical networks which require DWDM equipment and other such devices demand multiple amounts of splices and connectors. Splicing and connecting play a significant role in network cost and performance. Although mechanical splicing of optical fibers may be sufficient where there is no requirement for frequent connection and disconnection, current technologies for connectors or for splicing are still time consuming and expensive, since they are difficult to miniaturize and to manipulate. As well, there will be circumstances where connectors will be used in applications where flexibility for routing or reconfiguration is necessary or for connection of an end use device, such a computer or other electronic devices to a fiber or to other such devices. Current technologies for connectors or for splicing are still time consuming and expensive, since they are difficult to miniaturize and to manipulate.
As poor connection between the ends of two optical fibers will lead to signal distortion and loss of strength, a number of approaches have been proposed for proper optical fiber connections which will provide a good signal conduction. One such approach is set out in our international patent application entitled “A Connector for Optic Fibers” and published as WO 2004/015473. This application is incorporated herein by reference in its entirety.
In our aforesaid application, we propose a connector for connecting the ends of two optical fibers by abutment, wherein the connector is divided into a plurality of fingers, that extend longitudinally at each end and a fiber conduit extending from the first end to the second end. Such a connector is manufactured from Shape Memory Material (SMM), such as polymers, ceramics, or a metal alloys. In general, such materials when deformed at low temperature from a rest condition by mechanical deformation will then be biased to return to the rest condition when one heats them up over a temperature specific to the material used.
Use of such an optical fiber connector as described above is however not totally satisfactory as during the step of cooling or release of stress, there may be a tendency for the connector to push the ends of the optical fibers apart slightly. This makes it necessary during the operation of connecting optical fibers ends to include an additional step of restraining the optical fibers in a fixed position during the step where the connector returns to its original size, to prevent the optic fibers from being moved apart on the heating of the connector. Accordingly, some form of fixed clamping is required, of the buffer that typically covers and protects an optical fiber or bundle of such fibers to prevent axial movement of the optic fibers being connected. Such a step is cumbersome to the easy and quick connection of optical fibers using an aforesaid connector, requiring a certain degree of operational skill on the part of the technician carrying out the operation.
Although a Shape Memory Material (SMM) connector, as described in our international patent application published as WO 2004/015473, provides an improved means for connecting optical fibers, this still requires the use of certain operational skill by a technician carrying out the operation. As well, there is a need for improvement, such as in attenuation and return loss, fiber-to-fiber contact, dust accumulation and the like, in relation to optical fiber connection with ferrules, despite the common use of such technology in the field of optical signal transmission. Thus, there is a continuing need for an optical fiber connector assembly that is simple and quick to install and use and to maintain a good signal conduction between optical fibers, as well for a connection to be made and provided at a near end use device.
For purposes of the present application, with respect to Shape Memory Material (SMM), reference may be made to AFNOR Standard “Alliages à mé moire de Forme—Vocabulaire et Mesures” A 51080-1990, herein incorporated entirely by reference.
Shape Memory Materials (SMM) are characterized by the following behaviour when the material is below a temperature (Mf), which is a property dependent on the particular SMM, it is possible to strain (deform) the material. The strain is quite easily obtained by stressing the material with a relatively low stress. When stress is released, SMM retains the greatest part of the strain. When the SMM is heated above a second temperature (Af), which is also dependent on the particular SMM, the SMM will recover the strain. The recovery of strain is total unless the stress used to deform SMM exceeds the yield strength of the material. Thus, depending on the SMM, maximum recoverable strain reaches eight to ten percent. This shape memory phenomenon can be used to move or to stress other parts. During heating above (Af), the SMM can exert a strength. In such a way, strain recovery will be reduced, depending on the strength exerted. The higher the strength, the more the strain recovery will be partial.
At a very high strength, strain recovery will be null. If unstressed, the SMM will tend towards total recovery of its original shape. SMM also exhibits a pseudo-elastic properties coming from its shape memory characteristics. Pseudo elastic property is also referred togas super elastic effect.
The pseudo-elasticity results from the following phenomenon: when the SMM is at a temperature greater than (Af), it can be strained at particularly high rates, that is exhibiting unusual elasticity, arising from the shape MEMORY properties. Initially, when the SMM is stressed the strain will increase linearly, as in an usual elastic material.
However, at an amount of stress, called Sms, which is dependent on the particular SMM and temperature, the ratio of strain to stress is no longer linear, since strain increases at a higher rate as stress increases at a lower rate. At a higher level of stress, the increase in strain will tend to become smaller. On the release or reduction of stress, the reduction in strain will follow a different curve from the one manifested as stress was increased, in the manner of a hysteresis like loop.
An example of such an above material would be a shape memory alloy (SMA). Examples concerning activation of the shape memory element in a SMA include D. E. Muntges et al., “Proceedings of SPIE”, Volume 4327 (2001), pages 193-200 and Byong-Ho Park et al., “Proceedings of SPIE”, Volume 4327 (2001), pages 79-87. Miniaturized components of SMA may be manufactured by laser radiation processing. See, for example, H. Hafer Kamp et al., “Laser Zentrum Hanover e.v.”, Hanover, Germany [publication]. All of the above references are incorporated herein by reference.
Materials, which are suitable for the present invention, will illustrate pseudo elastic effect. SMM technology is particularly suited to optical fiber connection, as it offers:                a) a high strain capability allowing a sufficient enlargement of the bore diameter to freely insert the optical fibers;        b)-mechanical retention of fibers; and        c) allows to create a strength of abutment between the faces of fibers.        
The ferrule may, for example, be made from a shape memory polymeric material, such as isostatic polybutene, shape memory ceramics such as Zirconium with some additions of Cerium Beryllium or Molybdenum, or shape memory alloys: Copper alloys including binary and ternary alloys, such as Copper-Aluminium alloys, Copper-Zinc alloys, Copper-Aluminium-Beryllium alloys, Copper-Aluminium-Zinc alloys and Copper-Aluminium-Nickel alloys, Nickel alloys such as Nickel-Titanium alloys and Nickel-Titanium-Cobalt alloys, Iron alloys such as Iron-Manganese alloys, Iron-Manganese-Silicon alloys, Iron-Chromium-Manganese alloys and Iron-Chromium-Silicon alloys, Aluminum alloys, and high elasticity composites which may optionally have shape memory metallic or polymeric reinforcement.
With respect to the present invention, two optical fibers must be prepared so that the buffer is retrieved on a sufficient length to allow the ferrule to keep the claddings and cores in front of each other. A cleaving tool will advantageously cleave the ends of the optical fibers such that the extremities are flat and nearly perpendicular.
To connect the ends of two optical fibers using the ferrule connector, the connector must be first deformed to enlarge the diameter of its bore, which in its rest position is slightly smaller than the optical fibers. One end of the optical fiber is inserted into the bore of the ferrule and then a second optical fiber is inserted into the other end of the bore of the ferrule until the fibers face one another. An optical gel may also be applied, which have substantially of the same index of refraction as the optical fibers to assure uniform optical properties across the connection between the fibers.
Once the optical fibers ends are fully inserted into the connector, and the respective ends abut, the force applied on the connector may then be released and the connector allowed to shrink on the inserted fibers. Upon release of the force on the connector, the connector will then tend to exert a controlled compressive force on the optical fibers, sufficiently strong to retain the optical fibers in an abutment position but small enough not to damage the optical fibers by compression.